The present invention relates generally to statistical multiplexing schemes for digital cable and satellite television signals. More specifically, the present invention provides methods and apparatus for statistical multiplexing of a large number of video channels using a distributed, multistage multiplexing architecture. The present invention is particularly applicable to any dense multiplexing scheme, for example systems that require statistical multiplexing of approximately 250 video channels.
Digital television offers viewers high quality video entertainment with features such as pay-per-view, electronic program guides, video-on-demand, weather and stock information, as well as Internet access and related features. Video images, packaged in an information stream, are transmitted to the user via a broadband communication network over a satellite, cable, or terrestrial transmission medium. Due to bandwidth and power limitations, efficient transmission of film and video demands that compression and formatting techniques be extensively used. Protocols developed by the Motion Pictures Experts Group (MPEG) such as MPEG-1 and MPEG-2 maximize bandwidth utilization for film and video information transmission by adding a temporal component to a spatial compression algorithm.
Commonly, it is necessary to adjust a bit rate of digital video programs that are provided, e.g., to subscriber terminals in a cable television network or the like. For example, a first group of signals may be received at a headend via a satellite transmission. The headend operator may desire to forward selected programs to the subscribers while adding programs (e.g., commercials or other content) from a local source, such as storage media or a local live feed. Additionally, it is often necessary to provide the programs within an overall available channel bandwidth. It may also be desired to change the relative quality level of a program by allocating more or fewer bits during encoding or transcoding.
Accordingly, the statistical multiplexer (statmux), or encoder, which includes a number of encoders for encoding uncompressed digital video signals at a specified bit rate, has been developed. The statistical remultiplexer (statremux), or transcoder, which handles pre-compressed video bit streams by re-compressing them at a specified bit rate, has also been developed. Moreover, functions of a statmux and statremux may be combined when it is desired to transcode pre-compressed data while also coding uncompressed data for transport in a common output bitstream. Uncompressed programs are coded for the first time, while compressed programs are re-encoded, typically at a different bit rate.
These statmux and statremux devices evaluate statistical information of the source video that is being encoded, and allocate bits for coding the different video channels accordingly. For example, video channels that have hard-to-compress video, such as a fast motion scene, can be allocated more bits, while channels with relatively easy to compress scenes, such as scenes with little motion, can be allocated fewer bits. An example of a statistical multiplexing scheme is disclosed in, for example, commonly-owned co-pending patent application Ser. No. 09/665,373 filed on Sep. 20, 2000 entitled Method and Apparatus for Determining a Bit Rate Need Parameter In A Statistical Multiplexer, which is incorporated herein and made a part hereof by reference.
As the number of services offered over cable and satellite television systems continue to grow, there has developed a need for improved multiplexing schemes that can accommodate the dense multiplexing required to deliver such a large number of services. It would be advantageous to provide a practical method to statistical multiplex a large number of video channels using a distributed, multistage multiplexing architecture.
The methods and apparatus of the present invention provide the foregoing and other advantages.